Here the 1852 LDS edition changed the singular word to words, probably unintentionally. This reading has been followed by all subsequent LDS editions. We have already discussed quite a few cases where there has been some variation in the grammatical number for word(s). For some discussion regarding “the word(s) of the Lord”, see under Mosiah 20:21; for the phrase “the word(s) of God”, see under Alma 5:11. Either number for word is possible when referring to the Lord, although the singular dominates in the Book of Mormon text. In each case, the critical text will follow the earliest extant reading, thus the singular word here in Helaman 6:36. See under Helaman 16:1 for specific discussion of the expression “to believe in the word(s) of the Lord”.
Summary: Restore the singular word in Helaman 6:36, the reading of the earliest text; either singular or plural is possible, but the singular form is the more frequent one in referring to the word(s) of the Lord.